The present invention relates to an installation position of a damper in industrial vehicles such as forklifts.
Generally, in forklifts, a rear axle supporting rear wheels is pivotally attached to a vehicle frame by a center pin. A damper, which is a hydraulic cylinder, is located between the vehicle frame and the rear axle. When the vehicle travels on a bumpy surface, the damper extends and contracts to permit a pivotal movement of the rear axle. This suppresses inclination of the vehicle and improves the stability of the vehicle.
When the vehicle turns, the vehicle may be excessively inclined by a centrifugal force applied on the vehicle body. As a measure against this, Japanese Unexamined Patent Publications NOS. 9-309308, 9-309309 describe a technology for locking the damper based on detection of the vehicle""s turning state to limit the pivotal movement of the rear axle.
The vehicle frame has a box-structure for strength. However, to produce a space for accommodating the rear axle and the rear wheels, the sectional area of the vehicle frame is smaller toward its rear. Thus, the strength of the vehicle frame is relatively weak in the vicinity of the rear axle. Further, a force is applied to a part of the frame at which the upper end of the damper is attached. When the damper is locked, a much greater force is applied to the part.
To receive the force of the damper, the upper end of the damper should be attached to a stronger part of the frame, that is, the front part where the sectional area is greater. As one option, a bracket may be extended from the rear axle to the front part of the vehicle frame, and the lower portion of the damper may be supported by the bracket. In this way, the damper is located toward the front part of the frame, and the upper portion of the damper can be attached to a forward part of the frame. As a second option, the axis of the damper may be inclined to extend from the rear axle toward the front part of the frame. In this case the lower portion of the damper is supported on the rear axle, and the upper portion of the damper is attached to a forward part of the frame.
However, in the first option, a load may be applied from the frame to the bracket, and the bracket may be deformed by the force. This may apply a bending force to the damper, thus disturbing the operation of the damper. Therefore, the bracket must be strong, which increases the size of the bracket. Also, since the bracket projects frontward from the rear axle, the rear wheels may interfere with the damper or the bracket when the rear wheels are turned to the maximum angle. This limits the range of steering of the rear wheels.
In the second option, the axis of the damper crosses a plane perpendicular to the pivoting axis of the rear axle. Therefore, when the rear axle pivots, a torsion force and a bending force are applied to the damper. The torsion force applies a deforming force to the connecting parts between the damper, the rear axle, and vehicle frame. The bending force disturbs the optimal operation of the damper. Therefore, the damper must be strong to withstand the torsion and bending forces, which increases the size of the damper.
An objective of the present invention is to provide a structure for desirably arranging a damper between a rear axle and a vehicle frame.
To achieve the above objective, the present invention provides an industrial vehicle having the following structure. A frame includes a forward end and a rearward end. A rear axle is pivotally joined to the frame about a pivot axis. A pair of supporting members support the frame on the axle. The supporting members are intersected by a vertical plane that includes the pivot axis. A damper is located between the frame and the axle. The damper has a longitudinal axis. An upper end of the damper is connected to the frame and a lower end of the damper is connected to the axle. A bracket is located on the frame to receive the upper end of the damper. The bracket is located no further forward than the front supporting member and no further rearward than the rear supporting member.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.